1. Field of the Invention
The present invention relates to a lithium nickel manganese cobalt composite oxide used as a cathode active material for a lithium rechargeable battery, a manufacturing method thereof, and a lithium rechargeable battery using the composite oxide as a cathode active material.
2. Description of Related Art
Conventionally, lithium cobalt oxide has been used as a cathode active material for lithium rechargeable batteries. However, since cobalt is rare metal, a lithium nickel manganese cobalt composite oxide with low cobalt content (e.g., Related Arts 1 and 2) has been developed.
In recent years, batteries having a superior rapid charge characteristic are in demand for electric automobiles and electric power tools. One of the methods for enabling rapid charging is to increase a specific surface area of a cathode material. However, the conventionally developed lithium nickel manganese cobalt composite oxide has a small specific surface area.
Many of conventional methods for synthesizing a lithium nickel manganese cobalt composite oxide use a nickel manganese cobalt composite hydroxide as a parent material. However, this material also has a small specific surface area, and therefore the resulting lithium nickel manganese cobalt composite oxide has a small specific surface area.
Meanwhile, a method using a manganese cobalt composite carbonate as a parent material has been proposed. Related Art 3 discloses a manufacturing method of a nickel manganese cobalt composite carbonate in which a solution containing a sulfate of nickel, manganese, and cobalt and an aqueous solution containing an ammonium bicarbonate are simultaneously or alternately added to a solution containing water by a falling-drop method while maintaining pH of the mixture at 6.5-8.5, so as to cause a reaction. Related Art 4 discloses a method in which a solution containing a sulfate of nickel, manganese, and cobalt and an aqueous solution containing a sodium carbonate are simultaneously added to a solution containing water, so as to cause a reaction.
However, the composite carbonate obtained by the methods disclosed in Related Arts 3 and 4 has a low tap density of less than 1.7 ml/g, while having a BET ratio surface area of equal to or larger than 40 m2/g. Therefore, the lithium nickel manganese cobalt composite oxide generated by using the composite carbonate has a problem of a low filling density in a cathode active material when an electrode is created.
In addition, it has been desired that a lithium rechargeable battery using a lithium nickel manganese cobalt composite oxide as a cathode active material have enhanced battery performance, in particular, cyclic and load characteristics.
[Related Art 1] International Publication No. WO 2004/082046 pamphlet
[Related Art 2] International Publication No. WO 2005/020354 pamphlet
[Related Art 3] Japanese Patent Laid Open Publication No. 2001-148249, pages 7 and 9
[Related Art 4] Japanese Patent Laid Open Publication No. 2006-117517, page 7